The present invention relates in general to a device for separating water and filtering pollutants from liquid hydrocarbons, particularly a gas fuel. The device is of the type having a substantially horizontal housing enclosing at least one cylindrical filtering and coalescing element and at least one cylindrical water separating element, the elements being arranged in horizontal direction parallel to each other. Liquid hydrocarbons flow from an inlet port at one end of the housing into the filtering and coalescing element from which they are discharged into the interior of the housing and enter from the outside the water separating element from which they are discharged into an outlet port arranged at the same one end of the housing.
Conventional devices of this kind which are also designated as filtering water separators, serve for a very fine filtration and separation of free water particles, that means particles which are not dissolved in hydrocarbons. Such devices are employed in mobile or stationary fuel filling stations such as a gassed fuel, for example. In such stations, very high standards are to be met as regards the filtering quality and the phase separating quality of the employed filtering and separating elements. Further fields of application of such devices are for example in chemical, particularly in petrochemical industry.
In the known device, the first stage consisting of one but mostly of a plurality of filtering and separating elements, the emulsion containing water and liquid hydrocarbons is broken down whereby finely divided water particles coalesce into large drops. At the same time, the finest pollutant particles are filtered.
In the second stage consisting of one or more separating elements there are employed boundary surface materials of separating or dissociating quality, such as hydrophobic materials which are impermeable to water but permeable to hydrocarbons so that water drops are blockhead before the inflow of the hydrocarbon liquid into the separating element. The separated water drops are collected in a sump basin at the bottom of the housing and are periodically withdrawn therefrom.
The application of such devices in mobile fuel filling equipment necessitates a space-saving construction which at the same time permits a high through-flow rate. Inasmuch as extremely high filtering efficiency and particularly high water separating efficiency is required, the design of the flow conditions and flow distribution in the interior of the housing and primarily along the cylindrical filtering and coalescing elements and along the separating elements is of great importance.
From the contradictory requirements that a high flow rate of the fuel is to be achieved and at the same time any entrainment of water particles into the separating elements due to the excessive flow is to be prevented, it has been found during the development of a known device of this kind (German Pat. No. 1,645,749) that a substantially uniform flow rate of the treated liquid is to be adjusted over the entire length of the separating elements. Conventional devices of this type use a vertical orientation of the separating elements and in order to achieve such a uniform flow a hollow cylinder was inserted into the separating element which at one end thereof was closed by the lid of the separating element and at its other end was in communication with the outlet port of the housing whereby the jacket of the hollow cylinder was provided with a plurality of inlet openings decreasing in size from the closed end to the outlet end.
The objectives of this above-described provision of the hollow cylinder in the separating element was to obtain a uniform through-flow rate over the entire upper surface of the separating element and from the standpoint of surface loads such uniform flow speed should be optimal. Nonetheless, the prerequisite condition is that a uniform flow toward the outer surface of the separating element and an unobstructed discharge of collected water on the upper surface of this element be always fulfilled.
In practice, however, the two preconditions are not met at all or are satisfied only insufficiently.
In view of present-day requirements to construct such devices with high through-flow efficiency at small size of the device, a very compact arrangement of the filtering and separating elements in the housing is necessary. The spacing between the individual elements is frequently only in the magnitude range of the diameter of water drops coalescing during the operation on the element. As a consequence, the sedimentation and the downward movement of the water drops are obstructed. The elements of the first stage which are mostly arranged in the lower part of the housing are superimposed in several planes, and for achieving the required flow rate, a relatively strong stream directed upwardly to the second stage is adjusted which counteracts the downward movement of the water drops. Furthermore, the fact is to be taken into consideration that the inlets of the filtering and coalescing elements in the first stage are always at one end of these elements and consequently the flow is not discharged uniformly over the entire length of these elements of the first stage but is stronger in the vicinity of the inlet end. Such a stream which is increased at one end of the elements in the first stage before impinging against the elements of the second stage diminishes the effectiveness of the aforedescribed measures applied to conventional devices in order to achieve a uniform flow rate.
Moreover, it is to be also considered that a uniform, radially directed flow attempted in prior-art devices contributes in considerable degree to compression of entrained water drops in perpendicular direction against the outer surface of the separating element so that these drops are effectively retained thereon. This retention, however, reduces the separating efficiency.